PARIS — Four months after the death of Slobodan Milosevic, a trial has opened of six of his top aides, a process that may finally render a verdict on Serbia's actions during the 1999 war in Kosovo.

The accused, all of them former Serb political and military leaders, will have to account for their role, if any, in a repressive campaign that led to the persecution and flight of nearly one million civilians.

Prosecutors said that Serbian forces, under the direction of Milosovec, then destroyed numerous villages and towns "to create an atmosphere of terror" and to drive out tens of thousands of unwanted Kosovo Albanians. An estimated 800,000 Kosovo Albanians fled and an estimated 7,000 to 9,000 people were killed.

The trial, which is expected to last more than a year, began early Monday in a crowded courtroom at the war crimes tribunal in The Hague.

The six accused represented almost all of Serbia's political and military leadership in 1999. Although Milosevic, the former Serbian president, was the undisputed strongman at the time, the six accused were part of his inner circle. They are providing prosecutors with the best remaining chance of obtaining a verdict on the 1999 events in the Serbian province of Kosovo.

During his own 4-year trial, which had not concluded at the time of his death, Milosevic appeared obsessed with Kosovo. He called it Serbia's historic heart and said it had to be kept under Serb control, since the rest of Yugoslavia had fallen apart.

In uncounted courtroom speeches, he maintained that Serbia had no choice but to combat the armed separatists of the Kosovo Liberation Army, which he called Western-backed terrorists.

Meanwhile, Kosovo's status as a United Nations protectorate remains unresolved. On Monday, the Serbian prime minister, Vojislav Kostunica, traveled to New York, hoping to convince the Security Council not to give independence to Kkosovo.

In the coming months, the trial may also offer an indirect look at the role of NATO in the 1999 war. When NATO launched its bombing campaign of Kosovo and Serbia, it was the first time in modern history that the Western alliance mounted what it called an armed "humanitarian" intervention for the purpose of saving a civilian population.

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Milosevic insisted that Serbs and Kosovars alike were victims of the NATO bombing and that the Kosovars fled NATO planes, not Serb guns. NATO's intervention also caused a number of civilian casualties, but they are not being examined by the court.

The six who lined up in the dock on Monday included two former politicians, Milan Milutinovic, a former president of Serbia and Nikola Sainovic, former Yugoslav deputy prime minister as well as four former generals, Dragoljub Ojdanic, Nebojsa Pavkovic, Vladimir Lazarevic and Sreten Lukic. All six have voluntarily surrendered to the tribunal and were allowed to wait at home until the trial began. Another former general, Vlastimir Djordjevic, who was to be part of the trial, is on the run; according to tribunal officials, he is living in Russia.

The six are charged with war crimes and crimes against humanity, including deportation, murder and persecution. All pleaded not guilty. Proceedings are dealing only with Kosovo and not with other atrocities in Croatia and Bosnia.

The case is one of the most complex currently being handled by the war crimes tribunal, where five trials are now going on, involving 17 accused.

Much of the evidence the prosecution will present is believed to be similar to that used in the Milosevic trial. But to obtain a verdict, prosecutors must demonstrate to the panel of three judges - from Britain, Pakistan and Bulgaria - that Belgrade had a "criminal plan" to expel forever a large portion of the Kosovo Albanians and, as prosecutors put it, "to change the ethnic balance of Kosovo."

The world has seen many images of , frightened Kosovo refugees flooding into Albania and on tractors, trailers, busses and trucks. But lawyers familiar with the proceedings said that to gain convictions, prosecutors must prove there was a Serb plan to expel them.

Prosecutors may resort to the evidence of insiders or to documents but admit they have few. They will try to prove their case by "inference," one of the lawyers said, by using the facts on the ground.

In his opening statement, the lead prosecutor presented a number of those facts: He said, "There was a clear plan directed from the top" to drive out ethnic Albanians.